Wireless Networks in industrial environments: State of the art and Issues Xavier Carcelle Member IEEE

Tuan Dang Member IEEE

EDF R&D – Department STEP 6, quai Watier 78401 Chatou Cedex FRANCE [email protected]

EDF R&D – Department STEP 6, quai Watier 78401 Chatou Cedex FRANCE [email protected], [email protected]

Abstract – Wireless is everywhere nowadays and WLAN (i.e. 802.11 standard family) has became used by almost any communications devices in the mass market. The recent achievements in the fields of transmission techniques, such as Spread Spectrum and OFDM, coding methods, such as Turbocodes, and channel multiple access methods, such as WCDMA has pushed the growing uses of reliable and low-cost wireless technologies. Among them the last standards are: IEEE 802.11 family (i.e. WiFi), HyperLAN and HyperLAN2, IEEE 802.15 (i.e. WPAN), IEEE 802.16 (i.e. WiMAX)… However, the industrial environments are not taken into consideration in the design of those standards, because its harsh constraints has specific characteristics (reliability, interferences with existing equipments, multi-path propagation, low-power consumption, real-time reconfiguration, security…) that need specific requirements and eventually standards. This paper will intent to give an overview of the wireless technologies and discusses the current and future possible technologies for the uses in the industrial environments (power plants and stations, factories, industrial buildings, automotive…). Our current works showed us that there is no perfect technology by it-self but the best trade-off solution is a hybrid architecture combining the right wired and wireless technologies Index Terms – Wireless, Wifi, IEEE 802.11, IEEE 802.15, IEEE 802.16, hybrid architecture, harsh environment, utility.

I. INTRODUCTION The last past years have been intense in terms of development of wireless standards and wireless applications. Those applications are going from mass market domestic uses including Internet access to industrial usage in the field of wireless sensors networks, wireless interconnection between computer based control devices (DCS, PLC…) and industrial asset management based on pervasive networks indoor or outdoor. These emerging wireless technologies can give benefits in cost-reduction, and reliability in industrial applications as well as opportunities in improving operational performance. But there is still work in progress to achieve usable technologies which meet industrial requirements. Firstly we will present an overview of the current and future wireless technologies from a standardization point of view. Secondly we will analyze the work to be done in the design and implementation in the industrial environments, such as in the utilities installations (power plants, sub-stations, factories). Finally we will present our current experimentations and future works within hybrid technology networking fields. 1-4244-9701-0/06/$20.00 ©2006 IEEE.

2. OVERVIEW OF WIRELESS COMMUNICATION TECHNOLOGIES A. Taxonomy and technical overview Wireless networking technologies can be divided into three main classes (see Figure 1). Each class addresses specific requirements and purposes in point-to-point and point-to-multipoint communication. WPAN addresses Personal Area Network in which most of the time, point-to-point communications are involved. However, point-to-multipoint communications are possible with wireless networks protocols such as PicoNET (based on Bluetooth) or ZigBee (based on IEEE 802.15.4b). The range performances are typically from 1 meter to a few dozens meters. The WPAN are designed for low data rate (usually 100-200 kbps). This family gather the following technologies: ZigBee, Bluetooth and UWB. WLAN addresses Wireless Local Area Networks where the main uses are inter-connecting high data rate applications (Multimedia streaming, files sharing…), building easy-todeploy HotSpot-like networks and lately Ad-Hoc enabled networks such as Mesh Networks. The range performances are typically from a few dozens meters indoor to a few hundred meters outdoor. The WLAN are designed for high data rate (usually 1 to 20 Mbps). This family is composed with WiFi and DECT. Finally WWAN addresses Wireless Wide Area Networks which are mainly focused for long-distance point-to-point high data rate connections. They are designed to link plant sites networks all together with date rate ranging typically over 10Mbps with distance performances over few hundred meters. This long-distance family gathers: WiMAN, WiMAX and Cellular networks. From a more technical point of view, wireless networks use a lot of underlying mobile communications technologies benefiting from digital signal transmission researches. The following tables present the technical characteristics of the different wireless standards with their respective frequencies and modulation issues. In term of frequency issues, the chapter III will cover the different regulations and the coexistence problems between each wireless technology. It intents to present a brief guideline that may help to make the right choice in industrial applications. In digital mobile communications systems, the modulation and the multiple access methods are important characteristics that has influence on the efficiency of the channel in terms of: data rate, robustness and power consumption. IEEE describes the robustness [1] as the degree to which a system

or component can function correctly in the presence of invalid inputs or stressful environment conditions. Robustness can also be achieved using MIMO systems. In communication theory, MIMO refers to radio links with multiple antennas at the transmitter and the receiver side. Given multiple antennas, the spatial dimension can be exploited to improve the performance of the wireless link. The performance is often measured as the average bit rate (bit/s) the wireless link can provide or as the average bit error rate (BER). Which one has most importance depends on the application.

Figure 3: Example of multi-carrier modulation. In Spread Spectrum communication, the baseband signal bandwidth is intentionally spread over a larger bandwidth by injecting a higher-frequency signal. So, energy used in transmitting the signal is spread over a wider bandwith, and appears as noise. Different Spread Spectrum techniques use different manners of injecting Pseudo Noise sequence (code) to distribute the power of the baseband signal. Below is an illustration of Direct Sequence Spread Spectrum technique [4].

Figure 4: Typical DSSS circuit. Following the standardized OSI model for wireless protocols, the physical (PHY) and the medium access (MAC) layers can be seen as below:

Figure 1: Wireless technologies taxonomy. Most of digital transmission system uses advanced channel coding technique to prevent errors in the transmission and to correct them in the receiver when they happen. Below (see Figure 2) is an example [2] of the encoding method for OFDM:

Digital Signal Processing (ex: OFDM encoder)

Network layer IEEE 802.11 (WLAN) IEEE 802.15.{3-4} (WPAN)

MAC

Sensor data

Antenna & Propagation issues

Transport layer

Multiple Acces s logic

Source / Channel coding

n-QAM or PSK Modulation

Figure 2: OFDM encoder. PHY

OFDM uses the principle of multi-carrier transmission technique that converts a serial high-rate data stream onto multiple parallel low-rate sub-streams. Each sub-stream is modulated on another sub-carrier. Below is an example of multi-carrier modulation with four sub-channels [3].

Channel coding or decoding

Modulation or Dem odulation

FEC (block coding, convolutional coding, Turbocode, …)

n-QAM or FSK or PSK…

Narrowband technique: OFDM

Spreading, des preading, s erial-to-parallel or parallel-to-serial…

Transmitter

Spread-spectrum technique:FHSS, DSSS…

Source

CSMA/C A (poss ible us e of other Ch. multiple access: TD MA, FDMA, CDMA)

Figure 5: PHY and MAC layers for wireless protocols. 1-4244-9701-0/06/$20.00 ©2006 IEEE.

Each digital signal transmission technique has its own advantages and drawbacks. Following is the comparison of the different Multi-Carrier narrowband Transmission and Spread spectrum Techniques: Transmission Technique FHSS (Bluetooth, DECT) DSSS (IEEE 802.11b, ZigBee, GSM)

OFDM (IEEE 802.11g, IEEE 802.11a )

Advantages

Frequency range

24022480 MHz

3.1-4.8 GHz

Channel bandwidth

1 MHz

Number of channels

79

1.368 GHz or 2.736 GHz or 528 MHz 2 or 13

Drawbacks

• robust to interference • strong with jamming

• limited data rate • higher power consumption

• support variable data rates • resistance to multi-path • resistant to narrow-band interferences Resistance to • link dispersion • multi-path • frequency interference • burst noise

• sensitive to jamming • limited number of same-cell access points

• higher power consumption • higher CPU needs

Figure 6: Comparison of different digital signal transmission techniques.

Multiple access

TDMA or CDMA

Peak data rate

723.2 kbps

Ultra Wide Band (Industrial environment)

802.15.1 802.15.3

“ZigBee”

Ultra Wide Band (HDR) (Offices environment)

Bluetooth

IEEE Standards

802.15.4 802.15.4

(WG a) (WG b) (WG a) 480 Mbps • 20 • 1 kbps Mbps (868 MHz ) • 40 kbps (915 MHz ) • 250 kbps (2.4 GHz)

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Powerconsumption Range performance Localization performance Security

Ternary CDMA or TFIOFDM

-

Impulse Radio

+++ +

+

++

+

++

+++

+

+++

++

+++

+++

+++

GFSK

B. WPAN (Wireless Personal Area Networks)

Wireless comm. technology

1 (868 MHz) 10 (915 MHz) 16 (2.4 GHz)

CSMA/ CA with FDMA and TDMA • BPSK/ • BPS QPSK K (DS(868/ SS 915 UWB) MHz ) • QPSK( MB• OQP OFDM SK ) (2.4G Hz) ++ +

Modulation

In the following paragraphs, we will analyse the characteristics of each class of wireless networking technologies:

• 2.4- 5.9-10.6 2.483 GHz 5 MHz • 902928 MHz (US) • 868.3 MHz (Eu) 5MHz 500MHz

• THPPM • TH-APAM

+

Figure 7: WPAN technologies. WPAN technologies are being quite heavily used these past years in the mass market industry but a very few in the industrial environment. The coming years will see a great spread out of these technologies in the factories and the industry in general. For instance the IEEE 802.15.4 working group is leading the technology standardization for such technologies matching the needs and the requirements.

C. WLAN (Wireless Local Area Networks) Wireless comm. technology Standards IEEE 802.11a Peak data 54Mbps rate Frequency • 5.15range 5.35 GHz (US) • 5.4705.725 GHz (Eu) • 5.7255.825 GHz (US/C hina)

Channel 20MHz bandwidth Number of 12 channels

WiFi

DECT

IEEE 802.11b 11Mbps

IEEE ETSI 802.11g 54Mbps 100kbps

• 2.42.4835 GHz (US/Eu ) • 2.4712.497 GHz (Japan) • 2.4465 2.4835 GHz (Fr) • 2.4452.475 GHz(S p) 20MHz

2.42.4835 GHz

20MHz

1.728MHz

3 (non overlappin g) CSMA/C A

3 (on overlapp ing) CSMA/ CA

10 (12 users per channel)

Multiple access

CSMA/C A

Modulatio n

• BPSK, • BPSK, • BPQ QPSK DQPS K, K QPS • 16QA (Heade K, M, r) 64QA • 16M • BPSK, 64Q QPSK( AM Payloa d) • CCK, PBCC ++ ++ ++

Powerconsumpti on Range +++ performanc e Security ++

• 18801900 MHz (Europe) • 18801990 MHz (Worldw ide)

FDMA/ TDMA GFSK

D. WWAN (Wireless Wide Area Networks) WWAN technologies is used mainly for two applications nowadays is cellular phone communications and wide range IP-networks such as inter-cities point to point links. The WiMAN technology for instance is high-data rate with range performances up-to several kilometers and no mobility. Whereas the cellular communications for data transfer are usually low-to-fair data rate with complete mobility in the covered areas with GPRS services. From an industrial point of view, the two cases can be found as applications. A far remote power plant can be connected to the corporate backbone using a long-distance IP-based connection like a 802.16 link retrieving data from a sensors. Also a GPRS modem can help to regularly access a remote sensors or enabling a power plant staff to stay connected to the corporate backbone while off-site for a manual metering or a measurement task. Wireless comm. technology Standards

++

++

++

++

Figure 8: WLAN technologies. WLAN technologies headed a huge development these pasts years with main applications such as Private LAN (Local Area Networks) and Public Internet Hot-Spots where

WiMAX IEEE 802.16a a:75Mbps e:15Mbps a:2-16GHz e:2-6GHz

Cellular Comm. GPRS 100kbps

Frequency range

10-66GHz

Channel bandwidth

20Mhz a:1.5-20MHz 25MHz(US) e:>5MHz 28MHz(Eu) a:1.5-20MHz e: under definition TDMA OFDM

usually 1.25MHz

QPSK, 16QAM,

QPSK, 16QAM, 64QAM

QPSK, HPSK

+++

+++

++

+++

+++

+++

+

+

++

+

++

WiMAN

IEEE 802.16 Peak data rate 134Mbps

Number of channels

++

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the WiFi technology is now embedded in any electronic device as one of the main features. DECT has been also extremely used in-the-homes and is now used in industrial environment for voice and data over the private phone system. For wide industrial environment, such as big factories, storage areas, docks or power plants, DECT might be a good to have a reliable, robust wireless private phone system but also add to this system data communications and emergency alarms using the worldwide ISM bands. The backbone linking the DECT base stations is usually wired.

Multiple access Modulation

Powerconsumption Range performance Localization

GSM bands

depends on service CDMA

performance Security

+++

+++

+++

Figure 9: WWAN technologies. III. 3. FREQUENCY REGULATIONS AND COEXISTENCE ISSUES A. Frequency regulations issues These below tables present a brief overview of the different frequency regulations for the wireless technologies discussed in the previous chapter:

B. HarLei architecture HarLei has a classical Industrial IT architecture as shown in Fig. 4. HarLei is based on COTS, as it would require to much manpower to develop and maintain such a system. But more important than the financial aspect is the reliability. These COTS have been used for years by many other utilities, and once the system is installed, nearly everything is parameterized, the risk of a development bug is reduced. The economic dispatching of the secondary control signal shown on Fig. 5. is an example of an advanced functionality implemented in the SCADA system.

C. HarLei communication infrastructure Harlei is distributed over three computer centers and two dispatching rooms to provide a main/backup functionality:
The main system is composed of two computer rooms and one dispatching.
The backup-system is composed of one computer center and one dispatching. In case of a site disaster in the main system location, the backup system would take over. These sites are linked with a dedicated redundant TCP/IP network. Links to external systems are secured by firewalls. The communication between SCADA and power plants or TSOs is based on IEC 60870-5-101(serial line) and IEC 60870-5-104 (IEC 60870-5-101 over TCP/IP) protocols. Each power plant is linked to Harlei over three dedicated communication lines (two for the main system, one for the backup system). The Data Master can be connected to external systems using SQL database links, CSV files or Web Services. This gives the system enough flexibility to be quickly linked to new external systems. D. The development of decentralized generation In Germany, the Renewable Energy Law (EEG) introduced a financial and physical nationwide compensation for renewable energy generation. The decentralized 1-4244-9701-0/06/$20.00 ©2006 IEEE.

generation is injected into the power grid and distributed in real time between the power producers [10]. The share of renewable energies in electricity consumption increased to 10.2 percent in 2005 [11]. In some situations (a windy summer night), renewable energy can be a big share of the power production. Actual wind forecasts have become essential to the generation dispatching, which reinforce the need for a highly available Data Master, but also highly available external systems. IV. CONCLUSION Although the liberalization of European power markets has begun in the beginning of 1996, it is not finished yet. The unbundling of European electric utilities requires the redeployment of telecontrol communication infrastructure and the development of new economic dispatch systems as a new electric energy landscape (deregulated structure) is drawn in which, TSOs are mostly not allowed to communicate directly with the power plants control centers in normal operating conditions. In this new market environment, IT has an important contribution to the reliability of power systems as the complexity is increasing in terms of information exchange and information volume. Of course, this open and evolving energy market had a big influence on Industrial IT. One immediate effect was the creation of new dispatching systems. A long term effect is the growing influence of economic optimizations on the traditional Industrial IT architecture. This also reinforces safety as one of the most important points of a generation dispatching, as downtime has economic consequences. Another influence of the liberalization is flexibility and anticipation. As the market evolves very quickly, the energy management systems must always be ready to provide new solutions in a very short period of time. The growing development of DER creates more and more disturbances to the historic power grid. In order to integrate DER , active and smart power systems are needed to create stability and to offer services to consumers and small/independent producers. V. REFERENCES [1]. [2].

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